(1) Field of the Invention
The present invention relates generally to fixtures for holding fiber optics, and more particularly to a fiber optic holder for mechanically holding and aligning many optical fibers that are to be processed in the high-vacuum environment required to form thin films onto the optical fibers' cleaved ends.
(2) Description of the Prior Art
To produce fiber optic mirrors which can be used as acoustic sensors, a totally or partially reflecting mirror must first be formed at the end of an optical fiber using thin-film deposition techniques. First, the fiber end is cleaved, polished and cleaned. A thin film of metal or metal oxide must then be deposited onto the end of the optical fiber. Typically, a sputtering deposition system is used to perform radio frequency (RF) sputtering or direct current (DC) sputtering in a high-vacuum chamber. While DC sputtering is the preferred technique for faster sputtering deposition of thin-film metals, RF sputtering is the preferred, albeit slower, sputtering technique for achieving a more uniform and smoother deposition of thin-film metals. RF sputtering is required for metal oxide thin-film deposition due to the nonconductivity of metal oxides. RF sputtering also allows the recombination of oxygen to any disassociated metal atoms from the metal oxide molecules during the sputtering process.
In general, these forms of thin-film deposition require an initial high vacuum (e.g., on the order of 10.sup.-1 torr) to ensure the purity of the optical-quality thin-film. Contaminants such as oil-type vapors, water vapor, unwanted gas molecules from air, etc., are greatly reduced by means of a very high vacuum. After the initial high vacuum has been achieved, a back pressure of about 5.times.10.sup.-3 torr of an inert gas, e.g., argon, is introduced into the vacuum chamber and maintained therein. However, regardless of the thin-film process employed, it is necessary to mechanically align and hold the optical fibers such that the thin-film processing can be achieved with repeatable accuracy.
One prior art approach to the problem of mechanical alignment of a plurality of fibers is to mold or pot the optical fibers in a fixture so that a fixed mechanical alignment is achieved. However, potting compounds frequently require hours or even days to cure. Further, the potting compound must be mechanically or chemically removed from the optical fibers after thin-film processing is completed. Another limitation of this approach is that most potting compounds are incompatible with a high-vacuum environment due to the outgassing of the potting compound vapors which usually contain volatile organic compounds. Thus, contamination of the tin-film deposition process is possible since the appropriate high vacuum cannot be used.
Another prior art approach to the problem of mechanically aligning a plurality of optical fibers is to clamp the fibers using a spring-loaded or screw-type compression clamping system. While providing ease of removal once the thin-film processing is complete, the use of mechanical clamping systems almost always introduces the risk of accidental abrasion or overstress of the optical fibers. The inflicted minor damage is frequently not discovered until the fiber is installed in its ultimate application where the fiber will eventually fail and break thereby necessitating time consuming and costly repair.